This invention relates to a liquid crystal display device, and more particularly to a homeotropic liquid crystal display device in which the optical anisotropy of a homeotropically oriented nematic liquid crystal layer is compensated for.
The homeotropic liquid crystal display device has been utilized and developed in various ways as liquid crystal display devices capable of representing clear displays.
A typical homeotropic liquid crystal display device comprises a homeotropic liquid crystal cell disposed between a pair of crossed polarizers.
Homeotropic liquid crystal molecules are oriented normal to the substrate surface (i.e. homeotropically) in the absence of an electric field. Then, the liquid crystal layer does not change the polarization state of the incident light. Thus, the incident light is cut off by the crossed polarizers, exhibiting "dark" OFF state.
When, for example, an a.c. electric field is applied to the liquid crystal layer, the liquid crystal molecules change their orientations. Then, there occurs annihilation of polarization or birefringence. Then, the incident light can transmit through the crossed polarizers to exhibit "bright" ON state.
When a cell of OFF state is seen along a direction normal or orthogonal to the substrate a substantially perfect dark state is obtained. However, with respect to the lights incident on the cell along directions off-set from the normal to the substrate, a perfect dark state can no more be obtained. Therefore, good visual recognition range of incidence angle is very narrow.
Generally, the most influensive factor for the grade of the display of the transmission type liquid crystal display device is contract.
For increasing contrast, it is necessary to decrease the light leakage in the dark state as far as possible. Thus, if a sufficiently dark state cannot be obtained in directions off set from the normal directions, as described above, the display grade should be extremely lowered.